1. Field of the Invention
The invention relates to a high-pressure pump that performs an intake stroke during which fluid is sucked into a pressurizing chamber and a pressurizing stroke during which the fluid in the pressurizing chamber is pressurized by reciprocating a plunger in a slide hole of a cylinder body and thus changing the capacity of the pressurizing chamber.
2. Description of the Related Art
For example, a high-pressure pump including a plunger is incorporated in a vehicle engine, which, for example, supplies fuel to fuel injection valves (refer to Japanese Patent Application Publication No. JP-A-2001-41129).
As shown in FIG. 15, the high-pressure pump includes a cylinder body 71, a plunger 73, a pressurizing chamber 74, a lifter 75, and a drive cam 76. The plunger 73 is inserted into a slide hole 72 of the cylinder body 71 such that it can reciprocate therein, and the pressurizing chamber 74 is provided at one end of the slide hole 72 (the upper end as viewed in FIG. 15). The lifter 75 and the drive cam 76 are provided at the other end of the slide hole 72 (the lower end as viewed in FIG. 15). The lifter 75 abuts on the plunger 73 at the inner bottom surface of the lifter 75 and reciprocates as guided by a lifter guide 77. The lifter 75 is urged by a spring 78 toward the drive cam 76. As the drive cam 76 rotates and the plunger 73 thus reciprocates in the slide hole 72, the capacity of the pressurizing chamber 74 changes, whereby fuel 79 is sucked into and pressurized in the pressurizing chamber 74.
Specifically, as the drive cam 76 rotates past a point where the plunger 73 is at the top dead center, the pushing force exerted by the drive cam 76 decreases, and the lifter 76 urged by the spring 78 moves down to the drive cam 76 side. During this, the capacity of the pressurizing chamber 74 gradually increases, and the fuel 79 is sucked into the pressurizing chamber 74 (intake stroke). On the other hand, as the plunger 73 rotates past a point where the plunger 73 is at the bottom dead center, the pushing force of the drive cam 76 increases, and the lifter 75 moves up to the pressurizing chamber 74 side against the urging force of the spring 78. During this, the capacity of the pressurizing chamber 74 gradually decreases, and the fuel 79 in the pressurizing chamber 74 is pressurized (pressurizing stroke). Then, the outflow of the fuel 79 from the pressurizing chamber 74 is interrupted by an electromagnetic spill valve 81 being closed in a pressurizing stroke, so that the fuel 79 is pressurized to a high pressure. When the pressure of the fuel 79 exceeds a specified value, a check valve 82 opens and the fuel 79 is discharged to the fuel injection valve side.
As shown in FIG. 16, a small space between the plunger 73 and a wall 83 forms a flow passage 84 of the fuel 79 discharged from the pressurizing chamber 74. The fuel 79 distributed via the flow passage 84 serves as lubricant and coolant and suppresses seizure due to heat generated by the reciprocation of the plunger 73.
In the high-pressure pump 85, when the pressure of the fuel 79 increases as the plunger moves toward the pressurizing chamber 74, a reaction force Fr caused by the pressure increase acts toward the drive cam 76. On the other hand, when the drive cam 76 pushes the lifter 75 upward and the plunger 73 moves toward the pressurizing chamber 74, a pushing force Fu acts from the drive cam 76 toward the pressurizing chamber 74.
The drive cam 76 contacts a center C of the lifter 75 at a base circle portion 76A. A contact portion Pa of the drive cam 76 at which it contacts the lifter 75 shifts and deviates from the center C of the lifter 75 as the drive cam 76 rotates. This causes the lifter 75 to incline within an allowable range corresponding to the clearance between the lifter 75 and the lifter guide 77, as shown in FIG. 16. When this occurs, the plunger 73, due to its moment, also inclines in a certain direction in the slide hole 72. When the plunger 73 thus inclines, pressing force (side force Fs) is exerted from the plunger 73 to an end portion Ep of the slide hole 72 in the pressurizing chamber side and to an end portion Ed of the slide hole 72 in the drive cam side.
According to the trend in recent years, the fuel discharge amount or the fuel discharge pressure of a high-pressure fuel pump like the fuel pump 85 described herein is often increased to improve the engine performance. However, in this case, there is a possibility that the side force Fs may increase. That is, to increase the fuel discharge amount of the fuel pump 85, it is effective to advance the close timing of the electromagnetic spill valve 81 to a point close to the bottom dead center. However, this increases the reaction force Fr caused by an increase in the pressure of fuel 79, and therefore increases the side force Fs. As a result, more heat is generated at the drive cam side end portion Ed and the pressurizing chamber side end portion Ep of the slide hole 72 as the plunger 73 slides in the slide hole 72. In this case, therefore, a large amount of fuel 79 is needed to prevent seizure. In the conventional high-pressure pump 85, however, since the volume of fuel 79 in the pressurizing chamber 74 is large, heat can be sufficiently released from the pressurizing chamber side end portion Ep that is close to the pressurizing chamber 74. However, there is a possibility that a sufficient amount of fuel 79 may not be supplied to the drive cam side end portion Ed that is far from the pressurizing chamber 74.
In the Japanese Patent Application Publication No. JP-A-2001-41129, the clearance between the plunger 73 and the wall 83 of the slide hole 72 is made larger in the pressurizing chamber 74 side than in the drive cam 76 side, so that the plunger 73 contacts the drive cam side end portion Ed prior to the pressurizing chamber side end portion Ep. However, no measures have been taken for the drive cam side end portion Ed. Therefore, there is still a possibility that the aforementioned problem may occur.